As far as measuring the three-dimensional shape of a non-textured target surface such as that of a metal is concerned, a phase shift method is known in which the three-dimensional shape of the target surface is measured by projecting a plurality of sinusoidal wave patterns having different phases onto the target surface; taking an image of the target surface having the sinusoidal wave patterns projected thereon; and calculating phases from the sinusoidal wave patterns captured in the image.
Another technology is also known in which RGB patterns having the phase shifted for each color channel are used as a plurality of sinusoidal wave patterns having different phases, and in which the three-dimensional shape of the target surface is measured by projecting a plurality of such sinusoidal wave patterns onto the target surface at once.
In the conventional technology mentioned above, if the target surface is smooth in nature and if the projected patterns are reflected to a satisfactory extent, then it is possible to measure the three-dimensional surface of the target surface. However, in case it is not possible to achieve satisfactory reflection of the projected patterns, then there are times when the phases of the projected patterns cannot be calculated in a correct manner from the image in which the patterns projected onto the target surface are captured. In such a case, it is not possible to measure the three-dimensional shape of the target surface.